Dimension measuring system using track reference targets to define left and right top-of-rail elevations

ABSTRACT

A dimension measuring system includes a target positioning system mounted on a railroad track&#39;s parallel rails. The target positioning system includes two targets positioned at fixed positions in a first plane perpendicular to the rails, and another two targets positioned at fixed positions in a second plane perpendicular to the rails and spaced-apart from the first plane. A laser-based distance measuring device measures vector distances to the four targets. A processor, coupled to the laser-based distance measuring device, determines an elevation of each of the rails in the first plane and second plane using the vector distances and the fixed positions of the targets in the first and second planes. The elevation of each the rails in the first and second planes define a top-of-rail reference plane used by the processor when dimensions of an object above the top-of-rail reference plane are to be measured.

This is a divisional application of co-pending application Ser. No.14/723,180, “TRACK REFERENCE TARGETS AND METHOD OF USING SAME TO DEFINELEFT AND RIGHT TOP-OF-RAIL ELEVATIONS”, filed on May 27, 2014.

FIELD OF THE INVENTION

The invention relates generally to dimensional measuring systems andmethods, and more particularly to a dimension measuring system usingtrack reference targets to define the left and right top-of-railelevations of a railroad track, determine the centerline of the railroadtrack, and determine the heights and widths of a load (commodity) thatis to be transported via railway car on the track.

BACKGROUND OF THE INVENTION

Measurement of an object's dimensions has typically been accomplished ina manual fashion using fixed-length rulers, adjustable-length rulers(e.g., tape measures), plumb lines, hand levels and combinationsthereof. Use of these various manual measurement tools becomes difficultand/or dangerous when object is large and/or irregular in shape, or islocated in an environment that is limited in terms of accessibility oris inherently dangerous.

In general, oversized loads must be measured prior to their movement byany land, water, and/or air-based vehicle for reasons of safety,efficiency, etc. Oversized loads transported over land (e.g., byrailroad, road travel, etc.) must be measured prior to being moved overa predetermined route in order to assure that the load can maintain safeclearance over the route. By way of illustrative example, this scenariowill be explained for railway freight. In general, railway freightshipments that exceed a standard geometric envelope are deemed oversizedand officially classified as “Dimensional” or “High-Wide-Loads” (HWLs).Each railroad typically has its own set of specifications for what isconsidered to be a HWL load. HWLs must be measured at points of originand interchange points in route to their destinations to ensure thatthey can be safely transported over a particular rail line's route.Typically, several personnel are necessary for measuring a singleoversized load.

The traditional method of measuring HWLs required personnel to eitherclimb onto the load and/or use a ladder to physically measure the highpoints and wide points of the load. The typical tools used in thecurrent measurement method include a tape measure, plumb line,carpenter's level, and variety of homemade tools to assist inspectors inmeasuring hard-to-reach high-wide points. Such manual measurements havea number of inherent limitations relative to accuracy, efficiency,standardization, documentation, and safety.

In terms of accuracy, there are a number of factors that contribute tomeasurement inaccuracies. For example, many HWLs have critical pointsthat are difficult to reach. As a result, inspectors must often makemultiple measurements to determine a single height or width at acritical point on the load. Recordation of these manual measurements canalso be the source of mathematical and transcription errors. Inaddition, field measurements are currently referenced horizontally tothe edge of the railcar and vertically to the deck of the railcar (whichis then referenced vertically to one point on top of a rail andhorizontally to a vertical projection of the railway car's centerline).This approach also makes the assumption that the center of a railcar isaligned with the centerline of the track. However, this assumption isnot true in the vast majority of cases thereby leading to horizontalerrors. Vertical errors arise because the current method assumes thatthe track is level and fails to account for uneven rail elevations.Further, the current method of measuring HWLs does not account for“humping” or “bellying” (positive or negative camber) of the railcardeck due to the weight of the load and/or the design of the railcardeck. Thus, the current method assumes that the railroad track is leveland the deck of the railcar is also level. Since no track or car deck isperfectly level, inaccurate height and width measurement calculationsare produced.

In terms of efficiency and safety, most HWLs require two or more peopleto make the measurements. The manual measurement method usually requirespersonnel to either climb onto the load and/or use a ladder tophysically measure the high points and wide points. Often, a man-lift orbucket truck is required to reach critical positions on the load wheredimensions are required. Climbing on the loads,positioning/repositioning ladders or bucket trucks are time-consumingtasks. Further, these pre-measuring steps expose personnel to trip/fallhazards on the deck of the railcar, slick surfaces during inclementweather, and overall difficulties in traversing loads due to thegenerally irregular shapes of HWLs. These combined inefficiencies of thecurrent method also negatively affect overall rail yard operations.During the measurement process, “blue flag” protection is usuallyrequired which means the track where the load is being measured isclosed. Moreover, if a ladder is used to measure the oversized load, itis often necessary to shut down adjacent tracks in addition to the trackwhere the load is sitting. This negatively affects the railroad'sability to efficiently assemble and switch trains thereby delayingshipments. Additionally, a single measurement error could result in aninefficient routing of the load or a clearance deficiency resulting in aderailment, collision, property damage, environmental damage or evendeath.

In an effort to improve the accuracy, efficiency, and safety associatedwith measuring HWLs that are to be transported via railroad tracks, alaser-based dimensional object measurement method and system has beendeveloped and is disclosed in U.S. Patent Publication No. 2013/0096875.Briefly, this reference discloses a method/system in which each of twotargets is attached to a railroad track using a bar-like mechanism. Thetargets are positioned at each end of a railway car that is supporting aload (commodity) to be measured. A laser-based distance measuring deviceis positioned within line-of-sight of the targets and the load to bemeasured. The laser-based measuring device is used to measure vectors tothe targets and vectors to positions on the load. The vectors to thetargets are processed to generate horizontal and vertical referencesbetween the targets. The vectors to positions on the load are processedin order to generate dimensions of the load in relation to thehorizontal and vertical references. While this system/method is asubstantial improvement over the manual measurement method, it ispredicated on an average top-of-rail height at a railroad track'scenterline. However, most railroad tracks' left and right rails are notat the same elevation such that a load thereon is tilted side-to-sideand/or front-to-back. For HWLs, this reality can lead to errors in aload's width or height that, in turn, can lead to an incorrect decisionrelated to the load's ability to be safely transported over a particularrail line route.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide adimension measuring system using track reference targets to define arailroad track's left and right top-of-rail elevations.

Other objects and advantages of the present invention will become moreobvious hereinafter in the specification and drawings.

In accordance with an embodiment of the present invention, a dimensionmeasuring system includes a target positioning system mounted on arailroad track's parallel rails. The target positioning system has afirst target, a second target, a third target, and a fourth target. Thetarget positioning system positions the first target and second targetat fixed positions in a first plane perpendicular to the rails whereinone of the first target and second target is positioned at a known andfixed height over one of the rails. The target positioning systempositions the third target and fourth target at fixed positions in asecond plane perpendicular to the rails and spaced-apart from the firstplane wherein one of the third target and fourth target is positioned ata known and fixed height over one of the rails. A laser-based distancemeasuring device measures vector distances to the first target, secondtarget, third target, and fourth target. A processor, coupled to thelaser-based distance measuring device, determines an elevation of eachof the rails in the first plane and second plane using the vectordistances, the fixed positions in the first plane, and the fixedpositions in the second plane. The elevation of each the rails in thefirst plane and second plane define a top-of-rail reference plane usedby the processor when dimensions of an object above the top-of-railreference plane are to be measured.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention willbecome apparent upon reference to the following description of thepreferred embodiments and to the drawings, wherein correspondingreference characters indicate corresponding parts throughout the severalviews of the drawings and wherein:

FIG. 1 is a partially exploded perspective view of a track referencetarget assembly in accordance with an embodiment of the presentinvention;

FIG. 2 is a perspective view of an embodiment of a track referencetarget assembly in an assembled state;

FIG. 3A is an isolated side view of a laser-receiving target inaccordance with an embodiment of the present invention;

FIG. 3B is an isolated side view of a laser-receiving target inaccordance with another embodiment of the present invention;

FIG. 4 is a side view of a track reference target assembly illustratingthe positioning of two reference targets in accordance with anembodiment of the present invention;

FIG. 5 is a side view of a track reference target assembly illustratingthe positioning of two reference targets in accordance with anotherembodiment of the present invention;

FIG. 6 is a schematic side view of a railway car-supported load, twotrack reference target assemblies positioned on a railroad track underthe railway car, and a laser-based measuring device and processor inaccordance with an embodiment of the dimension measuring system of thepresent invention; and

FIG. 7 depicts measurement geometry used to determine height and widthmeasurements of a point on a load that rests on the deck of a railwaycar in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, simultaneous reference will be made toFIGS. 1 and 2 where a track reference target (TRT) assembly inaccordance with an embodiment of the present invention is shown in apartially exploded form (FIG. 1) and in an assembled form (FIG. 2), andis referenced generally by numeral 10. As will be explained furtherbelow, TRT assembly 10 will be mounted to a railroad track's rails andis used to facilitate the determination of elevations for eachindividual rail as well as the centerline of a railroad track. Railelevations provide critical information used in calculating accurateload measurements for HWLs even when such measurements are made onnon-level railroad tracks. Non-level railroad tracks make a railway carlean that, in turn, makes it very difficult to manually measure loadwidth using conventional tools and methods that relay on plumb lines.Briefly, in an embodiment of the present invention, two TRT assemblies10 will replace the target mechanisms used in the laser-baseddimensional object measurement method and system described in theafore-referenced U.S. Patent Publication No. 2013/0096875, the contentsof which are hereby incorporated by reference.

TRT assembly 10 includes a rigid and linear base rail 12 that will bemounted to a railroad track's rails and a rigid and linear arm rail 14that is mounted to base rail 12. To simplify storage and handling of TRTassembly 10, each of base rail 12 and arm rail 14 can be made frommultiple pieces or be collapsible. For example, in the illustratedembodiment, base rail 12 is hinged at a central portion thereof asindicated by numeral 120. Similarly, arm rail 14 is hinged at a centralportion thereof as indicated by numeral 140. The particular hinging orcoupling mechanisms used for a multi-piece base rail 12 or a multi-piecearm rail 14 are not limitations of the present invention.

Base rail 12 has two rail-engaging shoes 121 and 122 mounted thereon.Shoes 121 and 122 are configured to securely engage the inside portionof a railroad track's rail as will be described in greater detail below.Shoe 121 is fixed to base rail 12 whereas shoe 122 is movably mounted tobase rail 12. By way of example, shoe 122 is mounted to a screw assembly123 on base rail 12. Screw assembly 123 is operated (e.g., via manualoperation using knob 124) to move shoe 122 towards or away from shoe 121so that base rail 12 can be secured to the inside edges of a railroadtrack's left and right rails. Accordingly, once base rail 12 is mountedon a railroad track's rails, the distance between the two shoe-to-railcontact points is equal to the width of the track (also known as “trackgauge”) at that location.

Base rail 12 provides two mounting locations for laser-receivingtargets. One location 125 is aligned with the portion of shoe 121 thatwill be aligned with the inside edge of one rail when TRT assembly 10 ismounted on a railroad track. The second location 126 is aligned andmovable with the portion of shoe 122 that will be moved into alignmentwith the inside edge of a track's second rail. Locations 125 and 126 candefine target receiving receptacles (e.g., tubes) for receiving the pinof a laser-receiving target. For example, FIG. 3A illustrates anexemplary target 20 having a base pin 22, a target swivel support 24coupled to base pin 22, and a target face 26 coupled to swivel pins 24Aof swivel support 24 that allows target face 26 to swivel about the axis24B defined by swivel pins 24A. Target face 26 can include cross-hair 28aligned with swivel axis 24B. In the illustrated embodiment, base pin 22fits into one of the tubes at locations 125 or 126 such that cross-hair28 defines location 125 or 126. Tube-to-pin engagement can include oneor more positive retention elements, the choice of which is not alimitation of the present invention.

FIG. 3B illustrates another exemplary target 30 having a magnetic base32, a target swivel support 34 coupled to magnetic base 32, and a targetface 36 coupled to swivel pins 34A of swivel support 34. Magnetic base32 allows target 30 to be readily positioned on a metal portion of arailway car for use in determining a railway car deck's centerline aswill be explained further below. Similar to target face 26, target face36 can include cross-hair 38 aligned with swivel axis 34B defined byswivel pins 34A. Swivel pins 24A and 34A can provide some swivelresistance so that the supported target face holds its swivel positionuntil positively re-positioned. When not in use, targets 20 and/or 30can be stored in base rail 12 as shown. Storage can also be provided inbase rail 12 for extra targets 20 and/or 30.

Arm rail 14 is rigidly coupled or mounted to base rail 12 at a fixedacute angle α, the particular choice of which is not a limitation of thepresent invention. Arm rail 14 is configured/constructed to allow atarget 20 (at location 126) to protrude therefrom and be visible afterarm rail 14 is coupled to base rail 12 as shown in FIG. 2. Theparticular construction of arm rail 14 that provides suchcoupling/mounting to base rail 12 is not a limitation of the presentinvention. The outboard end of arm rail 14 defines a location 141 (e.g.,using a tube receptacle) for the mounting of a laser-receiving target(e.g., target 20).

As mentioned above, TRT assembly 10 will be mounted to a railroad trackand used in conjunction with the above-referenced laser-baseddimensional measurement system. As will be explained further below, TRTassembly 10 can be configured and used to determine left and right railelevations of a railroad track when only one (nearest) rail is “visible”to the laser-based system or when both rails are visible. FIG. 4illustrates TRT assembly 10 mounted on parallel rails 102/104 of arailroad track 100 when only rail 104 is visible. FIG. 5 illustratesanother TRT assembly (comprising just base rail 12 with two targets 20)mounted on rails 102/104 when both rails are visible. The geometriesprovided by both TRT assemblies that make the determination of left andright rail elevations possible are also illustrated.

Referring first to FIG. 4 where it is assumed that only rail 104 isvisible, shoe 121 is positioned to abut the inside edge of rail 102 andshoe 122 is the moved (by turning knob 124) to securely abut the insideedge of rail 104. As a result, TRT assembly 10 is firmly coupled totrack 100. Arm rail 14 extends from base rail 12 at angle α as shown.Targets 20 are placed at fixed locations 126 and 141 where location 126is a known height over rail 104 and location 141 is known and fixedrelative to that of locations 125 and 126. Location 141 is outside theconfines of railroad track 100 and on the side thereof adjacent to rail104. The fixed geometries provided by the TRT assembly and this setupyield the following information:

-   -   a known and fixed horizontal distance H_(F) between target        location 125 and cross-hair 28 of target 20 placed at location        141;    -   a known and fixed vertical distance V_(F) between cross-hair 28        of target 20 at location 126 and cross-hair 28 of target 20        positioned at location 141;    -   a known and fixed vertical distance V_(T) between cross-hair 28        at target 20 at location 126 and top-of-rail 104;    -   a known and fixed angle α between arm rail 14 and base rail 12;    -   a horizontal distance H_(V) between cross-hair 28 of target 20        at location 126 and cross-hair 28 of target 20 at location 141        that is measured and will vary based on the position of shoe 122        owing to the track gauge; and    -   the width W_(T) of track 100 between rails 102/104 is defined        between locations 125 and 126 (i.e., H_(F)−H_(V)).        These known and fixed relationships are processed in combination        with vector distances (from a measuring device) to each of        targets 20 to determine the top-of-rail elevations of rails 102        and 104 at the intersection of the rails with the plane in which        the two targets 20 (i.e., the target cross-hairs) lie. For load        measurement scenarios requiring measurements to be made from        both sides of a railway car, a third target 20 can be positioned        at location 125, or arm rail 14 with target 20 affixed thereto        can be moved to the other side of base rail 12. In this way, the        original reference position of base rail 12 remains the same for        all measurements. The positioning of a third target 20 in        position 125, or the repositioning of arm rail 14 with its        target 20, provides the ability to establish the        three-dimensional spatial position of the laser measuring device        for continued measuring on the opposite side of the railway car        from the originating position of the laser measuring device.

Referring next to FIG. 5 where it is assumed that both rails 102 and 104are visible from the laser-based measuring device, arm rail 14 can beremoved from base rail 12 such that only base rail 12 is coupled/mountedto rails 102/104 in the same fashion as described above. In thisembodiment, the TRT assembly is defined when a target 20 is placed ateach location 125 and 126. The fixed geometries provided by this TRTassembly and this setup yield the following information:

-   -   the width W_(T) of track 100 between rails 102/104 is defined        between cross-hairs 28 of targets 20 at locations 125 and 126;    -   a known and fixed vertical distance V₁₀₂ between cross-hair 28        of target 20 at location 125 and the top of rail 102; and    -   a known and fixed vertical distance V₁₀₄ between cross-hair 28        of the target 20 at location 126 and the top of rail 104.        These known and fixed relationships are processed in combination        with the vector distances (from a measuring device) to each of        targets 20 to determine the top-of-rail elevations of rails 102        and 104 at the intersection of the rails with the plane in which        the two targets 20 (i.e., the target cross-hairs) lie.

In both of the above configurations, elevations of a railroad track'sleft and right rails (i.e., the top of each rail) can be accuratelydetermined. When both rails are visible from the laser measuring device,two of the TRT assemblies illustrated in FIG. 5 can be positioned atspaced-apart locations on a track with each TRT assembly locatedadjacent to a railway car's wheels. For this type of installation, thetop-of-rail elevations are readily determined using the known verticaldistances V₁₀₂ and V₁₀₄. However, since only one rail is typicallyvisible during a measurement session, FIG. 6 depicts a dimensionmeasurement scenario for a load measurement where only rail 104 isvisible. In this scenario, two fully-assembled TRT assemblies 10 toinclude arm rail 14 (as shown in FIG. 4) will be used. A railway car 200has its sets of wheels 202/204 on the rails of track 100. A load (e.g.,an HWL) 300 to be measured is on railway car 200. TRT assemblies 10 areplaced adjacent wheels 202/204 with one TRT assembly 10 being adjacentto wheels 202 and the other TRT assembly 10 being adjacent to wheels204. In this way, TRT assemblies 10 (and the measurements generatedusing same) are located where the weight of load 300 is displaced ontothe rails of track 100. In both of the TRT assembly configurations shownin FIGS. 4 and 5, each TRT assembly defines two fixed target locationsin a plane that is perpendicular to the rails of track 100. FIG. 6 alsoillustrates the attachment (e.g., magnetic attachment) of two targets 30to the side of either end of railway car 200 for use in determining thecenterline of railway car 200 as will be explained further below.

A laser-based measuring device 40 is used to measure vector distancesfrom device 40 to the cross-hairs on each of targets 20 on a TRTassembly. These vector distances in combination with the above describedknown/fixed parameters can be used (i.e., processed by a processor 42)to accurately determine a top-of-rail elevation of each rail of track100. Accordingly, the combination of the two TRT assemblies, measuringdevice 40, and processor 42 define a dimension measuring system. Thefour top-of-rail elevations define a top-of-rail reference plane thatwill be used for all load measurements. Since this reference planeaccounts for rail height variations, the outer dimensions of load 300can be accurately determined using perpendiculars to the referenceplane. Accuracy can be further enhanced by determining (viainterpolation) particular top-of-rail elevations at specific locationsalong load 300. That is, knowing top-of-rail elevations at each of TRTassemblies 10 provides the data needed to interpolate top-of-railelevations aligned with a particular location along a longitudinal axisof load 300 at which at critical dimensional measurement must be made.Note that the above-described reference plane can also be determinedusing two TRT assemblies configured as shown in FIG. 5 when both railsof a railroad track are visible.

Referring now to FIG. 7, measurement geometry made possible by thepresent invention is shown and will be used to describe how to determineheight and width measurements of a load (not shown) based on a point ofinterest “P” on the load that is resting on the deck (i.e., therectangle referenced by numeral 210) of a railway car (not shown). Forexample, a reflectorless laser-based measuring device (e.g., laser-basedmeasuring device 40) can be used to directly measure a vector distanceto point P. The railroad track's rails 102 and 104 are illustrated withdashed lines. The points labeled A₁₀₂, A₁₀₄, B₁₀₂, and B₁₀₄ are thetop-of-rail heights of rails 102 and 104 determined using two TRTassemblies (i.e., two of the TRT assemblies illustrated in FIG. 4 or twoof the TRT assemblies illustrated in FIG. 5) as described above. Thatis, the elevations A₁₀₂ and A₁₀₄ are determined by one TRT assemblywhose two targets lie in a plane that is perpendicular to rails 102 and104, and the elevations B₁₀₂ and B₁₀₄ are determined by one TRT assemblywhose two targets lie in another plane that is perpendicular to rails102 and 104. The height “H_(P)” of the load at point P is perpendicularand referenced to a line R-L between rails 102 and 104 under point P.The height of rail 102 at point R is determined by a straight gradeinterpolation between the top-of-rail elevations A₁₀₂ and B₁₀₂ alongrail 102. Similarly, the height of rail 104 at point L is determined bya straight grade interpolation between the top-of-rail elevations A₁₀₄and B₁₀₄ along rail 104.

The width “W_(P)” of the load at point P can be referenced to either thecenterline of the track (i.e., a line centrally positioned between andparallel to rails 102 and 104), or to the centerline “C_(L)” of deck210. Currently, several industry associations (to include the AmericanRailway Engineering and Maintenance-of-Way Association or AREMA) haverecommended that width measurements be made relative to the centerlineof a railway car's deck. Accordingly, centerline C_(L) will be usedherein to describe the determination of width W_(P) at point P.Specifically, width W_(P) is determined by doubling the perpendiculardistance “D” from point P to centerline C_(L). Determination ofcenterline C_(L) is accomplished by attaching targets 30 to both ends ofone side of railway car 200 as shown in FIG. 6. Since the center foreach of targets 30 is displaced from railway car 200 by a known/fixedamount, vector measurements to targets 30 can be used in combinationwith measurements of the width of railway car 200 at the locations oftargets 30 in order to determine centerline C_(L).

The advantages of the present invention are numerous. The TRT assemblyis a simple tool that enhances the load measurement capabilities of alaser-based load measurement system. Specifically, each TRT assemblypositions two targets in a known and fixed geometric relationship in aplane that is perpendicular to a railroad track's rails. As a result,the present invention's measurement process accurately determinestop-of-rail elevations (and center-of-track if needed) that can be usedas reference plane measurements when measuring/determining a load'sheight and width at critical points of interest. By starting withaccurate top-of-rail measurements, the present invention can be used todetermine accurate height and width measurements even when a railway caris leaning due to elevation differences in a railroad track's rails. TheTRT assembly is easily positioned/configured by a single operatorworking on the ground. The TRT assembly provides additionalmagnetically-mountable targets for placement on a railway car for use indetermining a railway car's centerline. Once the TRT assemblies are setup, measurements to targets and to various positions on a load can bemade. The system's processor can determine and report/display, forexample, “height above top-of-rail” or ATR as it is known, overallwidth, side of the railway car that the measurement was taken, anddistance from the laser measuring device to the point of interest aswell as provide the operator the chance to enter a description of thepoint measured. Measured points can be automatically sorted from highestto lowest ATR. The widest point measured and/or the last point measuredcan be automatically highlighted/noted.

Although the invention has been described relative to a specificembodiment thereof, there are numerous variations and modifications thatwill be readily apparent to those skilled in the art in light of theabove teachings. It is therefore to be understood that, within the scopeof the appended claims, the invention may be practiced other than asspecifically described.

What is claimed as new and desired to be secured by Letters Patent of the United States is:
 1. A dimension measuring system, comprising: a first track reference target (TRT) assembly having a first target and a second target, said first TRT assembly adapted to be positioned on a railroad track's parallel rails wherein said first target and said second target are at fixed positions in a first plane perpendicular to the rails, and wherein one of said first target and said second target is positioned at a known and fixed height over one of the rails; a second track reference target (TRT) assembly having a third target and a fourth target, said second TRT assembly adapted to be positioned on the railroad track's parallel rails wherein said third target and said fourth target are at fixed positions in a second plane perpendicular to the rails and spaced-apart from said first plane, and wherein one of said third target and said fourth target is positioned at a known and fixed height over one of the rails; a laser-based distance measuring device for measuring vector distances to said first target, said second target, said third target, and said fourth target; and a processor coupled to said laser-based distance measuring device for determining an elevation of each of the rails in said first plane and said second plane using said vector distances, said fixed positions in said first plane, and said fixed positions in said second plane, wherein said elevation of each the rails in said first plane and said second plane define a top-of-rail reference plane used by said processor when dimensions of an object adapted to be positioned above said top-of-rail reference plane are to be measured.
 2. The dimension measuring system as in claim 1, wherein said first TRT assembly positions said one of said first target and said second target outside the confines of the railroad track's parallel rails.
 3. The dimension measuring system as in claim 1, wherein said second TRT assembly positions said one of said third target and said fourth target outside the confines of the railroad track's parallel rails.
 4. The dimension measuring system as in claim 1, wherein said first TRT assembly positions said one of said first target and said second target outside the confines of the railroad track's parallel rails, and wherein said second TRT assembly positions said one of said third target and said fourth target outside the confines of the railroad track's parallel rails.
 5. The dimension measuring system of claim 1, wherein said first TRT assembly has a fifth target at another fixed position in said first plane, and wherein said second TRT assembly has a sixth target at another fixed position in said second plane.
 6. The dimension measuring system of claim 1, further comprising an additional target adapted to be coupled to each of opposing ends of a railway car positioned on the railroad track's parallel rails, the railway car having a deck of known width wherein, when said laser-based measuring device measures a vector distance to each said additional target, said processor determines a centerline of the deck of the railway car using said known width of the deck and said vector distance to each said additional target.
 7. A dimension measuring system, comprising: a first track reference target (TRT) assembly having a first target and a second target, said first TRT assembly adapted to be positioned on a railroad track's parallel rails wherein said first target and said second target are at fixed positions above the rails in a first plane perpendicular to the rails; a second track reference target (TRT) assembly having a third target and a fourth target, said second TRT assembly adapted to be positioned on the railroad track's parallel rails wherein said third target and said fourth target are at fixed positions above the rails in a second plane perpendicular to the rails and spaced-apart from said first plane; a laser-based distance measuring device for measuring vector distances to said first target, said second target, said third target, and said fourth target; and a processor coupled to said laser-based distance measuring device for determining an elevation of each of the rails in said first plane and said second plane using said vector distances, said fixed positions above the rails in said first plane, and said fixed positions above the rails in said second plane, wherein said elevation of each the rails in said first plane and said second plane define a top-of-rail reference plane.
 8. The dimension measuring system as in claim 7, wherein said first TRT assembly positions one of said first target and said second target outside the confines of the railroad track's parallel rails.
 9. The dimension measuring system as in claim 7, wherein said second TRT assembly positions one of said third target and said fourth target outside the confines of the railroad track's parallel rails.
 10. The dimension measuring system as in claim 7, wherein said first TRT assembly positions one of said first target and said second target outside the confines of the railroad track's parallel rails, and wherein said second TRT assembly positions one of said third target and said fourth target outside the confines of the railroad track's parallel rails.
 11. The dimension measuring system of claim 7, wherein said first TRT assembly has a fifth target at another fixed position in said first plane, and wherein said second TRT assembly has a sixth target at another fixed position in said second plane.
 12. The dimension measuring system of claim 7, further comprising an additional target adapted to be coupled to each of opposing ends of a railway car positioned on the railroad track's parallel rails, the railway car having a deck of known width wherein, when said laser-based measuring device measures a vector distance to each said additional target, said processor determines a centerline of the deck of the railway car using said known width of the deck and said vector distance to each said additional target.
 13. A dimension measuring system, comprising: a target positioning system adapted to be mounted on a railroad track's parallel rails, said target positioning system having a first target, a second target, a third target, and a fourth target, said target positioning system positioning said first target and said second target at fixed positions in a first plane perpendicular to the rails wherein one of said first target and said second target is positioned at a known and fixed height over one of the rails, said target positioning system positioning said third target and said fourth target at fixed positions in a second plane perpendicular to the rails and spaced-apart from said first plane wherein one of said third target and said fourth target is positioned at a known and fixed height over one of the rails; a laser-based distance measuring device for measuring vector distances to said first target, said second target, said third target, and said fourth target; and a processor coupled to said laser-based distance measuring device for determining an elevation of each of the rails in said first plane and said second plane using said vector distances, said fixed positions in said first plane, and said fixed positions in said second plane, wherein said elevation of each the rails in said first plane and said second plane define a top-of-rail reference plane used by said processor when dimensions of an object adapted to be positioned above said top-of-rail reference plane are to be measured.
 14. The dimension measuring system as in claim 13, wherein said target positioning system positions said one of said first target and said second target outside the confines of the railroad track's parallel rails.
 15. The dimension measuring system as in claim 13, wherein said target positioning system positions said one of said third target and said fourth target outside the confines of the railroad track's parallel rails.
 16. The dimension measuring system as in claim 13, wherein said target positioning system positions said one of said first target and said second target outside the confines of the railroad track's parallel rails, and positions said one of said third target and said fourth target outside the confines of the railroad track's parallel rails.
 17. The dimension measuring system of claim 13, further comprising: a fifth target at another fixed position in said first plane; and a sixth target at another fixed position in said second plane.
 18. The dimension measuring system of claim 13, further comprising an additional target adapted to be coupled to each of opposing ends of a railway car positioned on the railroad track's parallel rails, the railway car having a deck of known width wherein, when said laser-based measuring device measures a vector distance to each said additional target, said processor determines a centerline of the deck of the railway car using said known width of the deck and said vector distance to each said additional target.
 19. The dimension measuring system of claim 13, wherein a railway car having spaced-apart sets of wheels is positioned on the railroad track's parallel rails, and wherein said target positioning system is adapted to locate said first plane adjacent to one of the sets of wheels and is adapted to locate said second plane adjacent to another of the sets of wheels.
 20. A dimension measuring system, comprising: a target positioning system adapted to be mounted on a railroad track's parallel rails, said target positioning system having a first target, a second target, a third target, and a fourth target, said target positioning system positioning said first target and said second target at fixed positions above the rails in a first plane perpendicular to the rails, said target positioning system positioning said third target and said fourth target at fixed positions above the rails in a second plane perpendicular to the rails and spaced-apart from said first plane; a laser-based distance measuring device for measuring vector distances to said first target, said second target, said third target, and said fourth target; and a processor coupled to said laser-based distance measuring device for determining an elevation of each of the rails in said first plane and said second plane using said vector distances, said fixed positions above the rails in said first plane, and said fixed positions above the rails in said second plane, wherein said elevation of each the rails in said first plane and said second plane define a top-of-rail reference plane.
 21. The dimension measuring system as in claim 20, wherein said target positioning system positions one of said first target and said second target outside the confines of the railroad track's parallel rails.
 22. The dimension measuring system as in claim 20, wherein said target positioning system positions one of said third target and said fourth target outside the confines of the railroad track's parallel rails.
 23. The dimension measuring system as in claim 20, wherein said target positioning system positions one of said first target and said second target outside the confines of the railroad track's parallel rails, and positions one of said third target and said fourth target outside the confines of the railroad track's parallel rails.
 24. The dimension measuring system of claim 20, further comprising: a fifth target at another fixed position in said first plane; and a sixth target at another fixed position in said second plane.
 25. The dimension measuring system of claim 20, further comprising an additional target adapted to be coupled to each of opposing ends of a railway car positioned on the railroad track's parallel rails, the railway car having a deck of known width wherein, when said laser-based measuring device measures a vector distance to each said additional target, said processor determines a centerline of the deck of the railway car using said known width of the deck and said vector distance to each said additional target.
 26. The dimension measuring system of claim 20, wherein a railway car having spaced-apart sets of wheels is positioned on the railroad track's parallel rails, and wherein said target positioning system is adapted to locate said first plane adjacent to one of the sets of wheels and is adapted to locate said second plane adjacent to another of the sets of wheels. 